No one is suggesting that everyone with a weight problem has a mental illness.

But missing in the relentless drumbeat to "eat less, move more" is any public discussion about the role common mental health problems are playing in the obesity dilemma, observors say.

"We absolutely have not looked at this issue at all," says Dr. Valerie Taylor, chief psychiatrist at Toronto's Women's College Hospital.

"This is probably one of the number one reasons that we're not getting anywhere in terms of battling the obesity epidemic."

The relationship works both ways.

Fat tissue isn't inert. It's biologically active. It produces cortisol, a stress hormone, as well as inflammatory chemicals, both of which have been linked to mental illness. Cortisol is neuro-toxic. It can act on the brain in vulnerable people — putting them at increased risk for depression.

Conversely, people with depression produce excess cortisol. And one of the effects of cortisol on the body, Taylor and her colleagues recently reported in the Canadian Journal of Psychiatry, is a propensity to accumulate fat around the abdomen.

The interplay between obesity and mental health is complex, but "we have not had a public discourse on how tightly these two epidemics are linked," says Dr. Arya Sharma, professor of medicine and chair in obesity research and management at the University of Alberta.

Nowhere in the recent report from Canada's mental health commission is there a mention of obesity, he says. "And vice versa. With all the talk about healthy weights, there's a lot of focus on diet and exercise, but I don't see any focus on improving the mental health of our kids and our adults. And that is a huge part of what is really driving the obesity epidemic."

Studies have found that 66 per cent of those seeking bariatric, or weight loss surgery have had a history of at least one mental health disorder. Attention deficit disorder occurs in an estimated one in four. "These people really struggle with being able to eat healthy — they make impulsive choices, they can never make it to the gym, or they get to the gym, they've forgotten half their stuff," Taylor says. "If you get that illness under control they can be successful in losing weight."

Currently, 62 per cent of the nation's adult population is either overweight or obese, a trend that's tracking at an even faster pace among children and adolescents. Today, there are more overweight than "normal" weight Canadians, and the heaviest weight classes are growing the fastest.

In many cases, the weight gain happens so insidiously, people can't put their finger on exactly how it happened.

Humans have been hard-wired through evolution to eat as much, and as often, as we can, and the food industry, critics say, has done a formidable job creating extraordinarily seductive foods loaded in sugar and fat. Some of the world's leading addiction researchers believe today's highly processed foods interact with the brain in ways similar to cocaine or heroin.

It takes significant impulse control to resist the smorgasbord before us, "because your brain wants all of those things and can't get enough," says Sharma, who will be among the featured speakers at a three-day conference on obesity and mental health in Toronto later this month sponsored by the Canadian Obesity Network, the International Association for the Study of Obesity and the Centre for Addiction and Mental Health.

"Even the slightest problem with impulse control and decision-making is going to expose you, and make you much more likely to gain weight," Sharma said.

"I can't think of a single mental health problem which would not, in some form or fashion, contribute to weight gain, or make weight management extremely difficult for someone who has the genetics to put on weight."

Mood affects metabolism and changes the way the body responds to certain foods, he said.

Depression or bipolar disorder can cause changes in appetite, energy and motivation. Depression and anxiety cause play havoc with sleep, and the link between sleep problems and weight has never been stronger.

In a normal, sleep-wake cycle, leptin — the satiety or "I'm full hormone" that tells the brain to reduce food intake — increases, while ghrelin, which triggers appetite, decreases. That's so that people don't feel hungry when they're sleeping.

But when sleep is disrupted, the opposite occurs, Taylor's team wrote, so that people are not only awake, but they're also hungry.

Taylor says the links are also strong between adult obesity and abuse in childhood — emotional abuse, physical abuse and neglect. "Sexual abuse is probably the biggest one," she says. "Often times children incorrectly blame themselves for causing the abuse, so they want to change the way they look."

Psychiatric drugs — among the most commonly prescribed pills nationwide — are adding to the problem. Antipsychotics — medications that are now even being used for insomnia — can trigger "hedonic hyperphagia" — eating in pursuit of reward, rather than to ease hunger.

"With some drugs, they can put on massive amounts of weight," says Rohan Ganguli, professor of psychiatry and Canada Research Chair at the University of Toronto. One of his patients gained more than 100 pounds over the course of a year.

The drugs are often necessary. "But we have to mitigate risk," Taylor said. "We need to be aware of these side effects and prescribe correctly."

Food soothes anxiety and stress. It becomes a coping mechanism. Certain foods like carbohydrates can boost serotonin, which affects mood. For brief periods of time, we feel relaxed and comforted. But it doesn't last, and so people get into a cycle, Taylor says, "where they're constantly using food to feel better.

"We have to teach people how to stop doing that."

Taylor says she can't think of a more stigmatized group than those who have both obesity and mental illness. "Lots of times people don't come forward and say they have a psychiatric illness going on when they're looking for obesity treatment. Family doctors don't ask about it.

"We need to raise awareness. This is a complicated illness. It's not a blame thing. There are associations and things occurring that people aren't aware of," Taylor says.

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